Mineral Identification and Properties

The video tutorial discusses the characteristics of an igneous rock, focusing on its grain structure and mineral composition. It explains how to identify minerals like quartz, feldspar, and biotite mica using polarized light. The rock is classified as a porphyritic granifier, characterized by a ground mass of micrographic texture. The tutorial covers mineral properties, such as relief, extinction, and twinning, and explains the rock's formation from siliceous magma.

What is the typical size range of most grains in the igneous rock described?

• 2 to 4 millimeters

• 1 to 3 millimeters

• 0.1 to 1 millimeter

• 0.25 to 2 millimeters

Which mineral forms phenocrysts that are clear and do not change color when the stage is rotated?

• Feldspar

• Biotite mica

• Quartz

• Olivine

What term is used to describe crystals that show some crystal faces?

• Anhedral

• Subhedral

• Amorphous

• Euhedral

What causes the inbay quartz crystals to indicate that the quartz was not in equilibrium with the host magma?

• Cooling too quickly

• Superheating by mixing with hotter basaltic magma

• High pressure

• Presence of water

What appearance do feldspar phenocrysts have in plain polarized light?

• Opaque

• Brightly colored

• Cloudy or turbid

• Clear and colorless

How can you distinguish between types of feldspar under crossed polars?

• By their color

• By their size

• By their shape

• By the type of twinning shown

What is the color change observed in biotite mica when the stage is rotated through 90 degrees?

• Red to blue

• Yellow brown to darker green brown

• Green to purple

• White to black

What type of extinction does biotite mica show under crossed polars?

• Straight extinction

• Random extinction

• Inclined extinction

• Parallel extinction

What is the texture called that is characteristic of granifier?

• Phaneritic

• Aphanitic

• Porphyritic

• Micrographic

What are the main minerals making up the porphyritic granifier?

• Calcite, dolomite, and gypsum

• Muscovite, biotite, and chlorite

• Plagioclase feldspar, k feldspar, and quartz

• Olivine, pyroxene, and amphibole